This invention relates to a silica gel used for improving the haze stability of beer, a method of manufacturing the silica gel and a method of stabilization treatment of beer using the silica gel.
Conventionally, a method of stabilization treatment of beer using a silica gel which can prevent the generation of haze in beer is known. The preparation of a silica gel having various physical properties for use in the stabilization treatment is disclosed, for example, in the examined Japanese Patent Publication No. 63-38188 and the Japanese Patent laying-open Nos. 5-70120 and 5-97421.
However, since the conventional silica gels can insufficiently prevent a haze from being generated in beer, a large quantity of the silica gels are required for providing a desired effect, which increases the cost as well as the industrial wastes resulting from the manufacture of beer. Therefore, the physical property values of the silica gel, contributing to enhancement of the haze inhibiting effect, required to be strictly selected.
The specific surface area, the pore volume, the average pore diameter and other physical properties of the silica gel are dependent on one another: when either one of the physical properties change, the other ones also change. In the conventional art, even if a certain physical property is improved to increase the haze inhibiting effect, the other physical properties possibly change dependently to act against or lower the haze inhibiting effect, and, as a result, the silica gel provides only an insufficient haze inhibiting effect. Therefore, if the physical properties of the silica gel contributing to enhancement of the haze inhibiting effect are found and arc all improved when preparing the silica gel, the haze inhibiting effect could be remarkably enhanced.
An object of this invention is to provide a silica gel having the physical properties contributing to enhancement of a haze inhibiting effect improved in a well balanced manner.
Another object of this invention is to provide a method of manufacturing a silica gel which can prevent the generation of haze of beer.
A further object of this invention is to provide a method of stabilization treatment of beer using a minimum quantity of silica gels.
To attain these or other objects, the invention provides a silica gel for stabilization treatment of beer prepared by calcination at a temperature of 400-800xc2x0 C. between 10 seconds and 10 hours. The silica gel has a specific surface area of 700-1000 m2/g, a pore volume of 1.1-1.6 ml/g and a average pore diameter of 6-10 nm.
If the calcination temperature is lower than 400xc2x0 C., the silica gel provides an insufficient adsorbability. If the calcination temperature exceeds 800xc2x0 C., although the surface of the silica gel gains an improved quality, the specific surface area and the pore volume tend to be lowered because sintering is effected. Further undesirably, the specific surface area, the pore volume and the average pore diameter or other physical properties of the silica gel cannot be easily controlled to the optimum values required in the invention.
If the calcination time is shorter than 10 seconds, the quality of the silica gel surface can be improved only insufficiently. Even if the calcination time exceeds 10 hours, a further improvement in the surface quality cannot be expected and this is ineffective in cost.
According to the invention, the silica gel desirably has a large specific surface area. If the specific surface area is less than 700 m2/g, the silica gel cannot provide better adsorbability as compared with the conventional silica gel. However, the silica gel having a specific surface area greater than 1000 m2/g cannot be easily manufactured industrially, and this is not practical.
Furthermore, if the average pore diameter of the silica gel is less than 6 nm, the adsorbability of the silica gel remarkably deteriorates, while if the average pore diameter exceeds 10 nm, the specific surface area cannot be kept 700 m2/g or larger. Additionally, since the specific surface area, the average pore diameter and the pore volume are mutually dependent, the pore volume adequate for the industrial manufacture of the silica gel is between 1.1 ml/g and 1.6 ml/g while the average pore diameter and the specific surface area are controlled in the aforementioned ranges.
The present invention also provides a method of manufacturing a silica gel for stabilization treatment of beer. In the method, first a silica hydrosol is prepared by reacting silicate with inorganic acid such that the SiO2 concentration is between 10% and 20% by weight, and is gelled, forming a silica hydrogel. The silica hydrogel is washed with water, hydrothermally treated with water having a pH of 2-8 at a temperature of 20-100xc2x0 C. and acid treated with either inorganic or organic acid having a pH of 2-5. The washed, hydrothermally treated and acid treated silica hydrogel is ground into particles having a mean particle diameter of 5-30 xcexcm, dried at a temperature of 100-1000xc2x0 C. for 1-100 seconds, and calcined at a temperature of 400-800xc2x0 C. for 10 seconds to 10 hours.
The present invention further provides a method of stabilization treatment of beer, in which the aforementioned silica gel is contacted with beer, and subsequently is separated from the beer.
As aforementioned, according to the invention, the calcination temperature is between 400xc2x0 C. and 800xc2x0 C., the calcination time is between 10 seconds and 10 hours, the specific surface area ranges from 700 to 1000 m2/g, the pore volume ranges from 1.1 to 1.6 ml/g and the average pore diameter ranges from 6 to 10 nm. Both specific surface area and average pore diameter have relatively large physical property values. The inventors found as a result of their earnest researches that when a certain degree of average pore diameter is assured, the larger the specific surface area is, the more the adsorbability per unit weight increases, and adjusted and determined the manufacture conditions in order to increase both the specific surface area and the average pore diameter. In general, the silica gel having a large specific surface area tends to have a small average pore diameter. In this case, a haze causing component does not easily permeate the pores in the silica gel, the adsorptive surface area of the silica gel is not substantially large, and only insufficient adsorption effect can he obtained. According to the invention, however, the silica gel has a large adsorptive surface area and a relatively high adsorbability per unit weight. Therefore, even a small quantity of silica gels can provide an excellent haze inhibiting effect.
In the method of manufacturing silica gels according to the invention, the silica hydrosol is prepared by reacting silicate with inorganic acid such that the SiO2 concentration is between 10 and 20% by weight and gelled. Excessively low SiO2 concentration would lengthen the period of gelation time, increase water content, and deteriorate an efficiency in the subsequent washing and drying steps, which is industrially impractical. Excessively high SiO2 concentration could excessively accelerate the gelation process, and the silica hydrogel having uniform physical properties could not be obtained. As the silicate, sodium silicate, potassium silicate, ammonium silicate or other is available: sodium silicate is most used industrially. For the inorganic acid, sulfuric acid, nitric acid, hydrochloric acid or other is, available: sulfuric acid is generally used.
Subsequently, by washing the silica hydrogel with water, inorganic salt is removed. When the washed silica hydrogel is hydrothermally treated with water having a pH of 2-8 at a temperature of 20-100xc2x0 C., the average pore diameter and the pore volume are increased. In this process, if the silica hydrogel is washed with water under the conditions corresponding to those for the hydrothermal treatment, the washing and the hydrothermal treatment can be carried out simultaneously. For the conditions of the hydrothermal treatment, when the pH or the temperature is increased, the specific surface area tends to lower largely. When the pH or the temperature is lowered, the treatment time tends to be lengthened. Considering from these tendencies, the silica hydrogel is desirably hydrothermally treated at a pH of 6-8.5 and a temperature of 40-60xc2x0 C. Furthermore, the silica hydrogel is subsequently acid treated with either an inorganic or organic acid having a pH of 2-5, and obtains an increased average pore diameter and pore volume. In the hydrothermal treatment, primary particles of silica gel are solubilized and deposited, and the specific surface area of the silica gel is decreased while the average pore diameter and the pore volume are increased. In the aforementioned acid treatment, since the pH is set lower, the quantity of the solubilized and deposited primary particles is controlled, and only at the point where polymerizing primary particles touch each other, said primary particles combine with each other. Therefore, the specific surface area is quite gradually decreased while the average pore diameter and the pore volume are increased. The primary particles obtain an increased binding strength at the point where the primary particles combine with each other. The structure of the silica gel is stabilized and strengthened. If the pH is adjusted to 2 to 5 during the hydrothermal treatment, the treatment time is lengthened. However, since the conditions of the hydrothermal treatment meet these of the acid treatment, these treatment processes can be simultaneously carried out, thereby simplifying the procedure.
In other words, the water washing process, the hydrothermal treatment process and the acid treatment process can be serially carried out, or the first two or all the three processes can be executed at the same time. When the first two or all the three processes are simultaneously carried out, the treatment conditions need to be restricted within the range effective for each of the simultaneous processes, and such restriction may lengthen the treatment time as required.
The washed, hydrothermally treated and acid treated silica hydrogel has a relatively large average pore diameter, pore volume and specific surface area. Unless such large physical properties can be kept in the subsequent processes, the final product or silica gel with a large average pore diameter, pore volume and specific surface area cannot be obtained.
In order to maintain the large physical property values, according to the invention, the silica hydrogel is finely ground to form particles having an average particle size of 5-30 xcexcm, and dried at a temperature of 100-1000xc2x0 C. for 1-100 seconds. The grinding and drying processes can be carried out serially or simultaneously. The serially executed grinding and drying processes are desirable in that the physical property values can be easily controlled However, if these processes are executed simultaneously, the procedure can be simplifed. The drying process followed by the grinding process is undesirable because the pore volume of the silica gel may not be sufficiently large. Although the drying temperature and the drying time are set in inverse proportion to each other, in the drying process according to the invention, the particles are dried relatively rapidly and completely as compared with the conventional method of manufacturing silica gels. If the drying time is prolonged, the water content in the silica gel slowly decreases, the surface tension of water causes pore volume of the silica gel to be lower disadvantageously. In the invention, the particles are completely dried or dehydrated such that the surface area is prevented from decreasing or other physical properties are prevented from changing in the subsequent calcination process. Specifically, it is known that the adsorbability of silica gel used for stabilizing beer can be improved my the calcination process. If the silica gel contains water during the calcination process, the pore volume is decreased due to the surface tension of water, or the surface area is reduced because of hydrothermal polymerization (Ostwald aging). Especially, if the silica gel containing much water is calcined, the physical properties are remarkably changed. In the method of manufacturing the silica gel according to the invention, during the acid treatment, the pore structure of the silica gel is strengthened, and the acidified surface of the silica gel provides an enhanced heat resistance. During the rapid drying process prior to the calcination process, the water content of the silica gel is decreased. Therefore, even when the silica gel is calcined, the pore structure of the silica gel hardly weakens. In the present invention, also when the silica gel is finally calcined at a temperature of 400-800xc2x0 C. for 10 seconds to 10 hours, the average pore diameter and the pore volume of the silica gel are hardly lowered.
Consequently, the calcined silica gel having a large specific surface area and average pore diameter can be manufactured. Specifically, the calcined silica gel has a specific surface area of 700-1000 m2/g, a pore volume of 1.1-1.6 ml/g, and a average pore diameter of 6-10 nm.
In the stabilization treatment of beer according to the present invention, since silica gel has a high adsorbability, only a minimum quantity of silica gels are required for providing an excellent haze inhibiting effect. Therefore, the quantity of silica gels used can be reduced, cost can be saved, and industrial wastes from the manufacture of beer can be minimized.